1. Field of the Invention
The present invention relates to a device and a method for conveying fluid media.
2. Description of Related Art
For the cooling of electrical, electronic or micromechanical components and integrated circuits, the convection of liquid or gaseous fluids driven by turbo or displacement pumps is widespread. Through thermal diffusion, the recirculated fluid absorbs the heat at the hot, small surface of the component to be cooled and transmits it to a heat exchanger having a large surface in the form of thin lamellae or ribs on the system surface, usually the housing of the subassembly, which has excellent thermal conductivity. The media flow at the outer surface has an advantageous effect inasmuch as it counteracts boundary layer effects, which have an adverse effect on the heat transfer.
In comparison with the passive heat transfer via thermal diffusion, the (forced) coolant recirculation driven with the aid of pumps or fans requires a greater outlay in the construction. Furthermore, electrical or mechanical driving power is consumed, which therefore increases the overall power losses.
The cooling of electronic components such as output stage transistors and voltage converters as well as the cooling of highly integrated microprocessors and other digital circuits (ASICs) during operation at high clock rates is widespread and realized by the recirculation of air or water using displacement or turbo pumps (fans), in particular when high local power loss densities and thermally disadvantageous operating environments are involved. In addition to water and air, fuels or oils are also used as heat exchange media for the cooling of electronic control devices in machine plants or in engine and transmission control devices of motor vehicles.
The cooling of electronic engine control devices in the construction of motor vehicles by fuel recirculation, for example, poses high, cost-intensive demands on the long-term durability and long-term tightness of the pipes, pumps, valves and heat exchangers. Even the leakage of small quantities of fuel from the coolant circuit frequently causes the electronics to malfunction.
In addition, the passive fluid recirculation based on the principle of self-maintaining convection is known, especially the “heat pipe”, which is common in the area of computer electronics. This is a hermetically sealed system for the heat transfer, which uses evaporation cooling and self-maintaining coolant convection. The boiling temperature point of the fluid used lies in the thermal operating range of the heat source to be cooled. The liquid phase wets the inner wall of a thin pipe, and the gaseous phase, driven by the gas pressure in the interior of the pipe, is able to flow to the heat sink and dissipate the evaporation heat to a heat exchange element there by condensation. The thickness of the fluid layer wetting the inner pipe wall is restricted by the capillary effect, which allows only relatively small pipe diameters and therefore restricts the heat flow cross-section of the heat pipe.
Furthermore, electrical cooling using Peltier elements on the basis of the thermo-electrical Peltier effect is known. Such elements are made up of two interconnected semiconductors, whose lower conduction band edges lie at different energy levels. If an electrical voltage is applied across the boundary layer between the semiconductors, so that an electrical current is flowing from the semiconductor having the higher conduction band edge in terms of energy (heat source), to the semiconductor having the lower conduction band edge (heat sink) in terms of energy, then the flow of electrical conduction current will also be accompanied by a heat flow from the heat source to the heat sink. By relaxation, the electrons migrating from the heat source to the heat sink transmit to the lower conduction band edge a portion of their thermal excitation energy absorbed in the heat source, to the crystal lattice of the heat sink.
This thermoelectrically induced heat flow is counteracted by the heat diffusion; in addition, unavoidable Ohmic losses heat up the semiconducting materials. Thus, the thermal utilization factor of Peltier elements is low in comparison with other known cooling mechanisms. In addition, they themselves may possibly require more installation space than the electronic components to be cooled. Moreover, Peltier elements are relatively expensive and as a consequence are generally not considered for widespread use.